Lubricant is used in a wide temperature range from low temperatures to high temperatures. Accordingly, lubricant exhibiting a high viscosity index and a good low-temperature fluidity is required for a fluid dynamic bearing and an oil-impregnated bearing which are used in a motor such as a hard disk drive. Moreover, grease base oil exhibiting a high viscosity index and a good low-temperature fluidity is also required for grease used in a wide temperature range from low temperatures to high temperatures.
In response to such needs, various base oils have been proposed. For instance, a predetermined diester base oil exhibiting both of a high viscosity index and a low-temperature fluidity has been proposed to be used for lubricant and grease (see, for instance, Patent Literatures 1 to 3).